Multi-purpose and multi-function measuring instruments are known which measure more than one parameter or more than one order of magnitude and which require a logarithmic scale for one parameter and a linear scale for another. Such scales usually appear together on the face of the instrument and are swept by a pointer to give an analogue reading of the parameter being measured The user reads this magnitude off the scale which is known to have been selected. Such instruments are also known which provide a digital read-out and in this case the analogue magnitude which is measured is converted electronically to digital form and is electronically scaled to be logarithmic or linear or to represent the correct order of magnitude.
It is an object of the present invention to provide an improved scale for a measuring instrument which enables only one scale to be visible at a time and which enables a logarithmic function or a linear function to be displayed as required.